Heat exchanger conduit having internal fins



J. W. BROWN, JR

2 SHEETS-SHEET 1 INVENTOR. JOHN W BROWN JR.

flwmz/ ATTORNEYS.

Oct. 30, 1951 HEAT EXCHANGER CONDUIT HAVING INTERNAL FINS Filed April 10, 1947 1 J. w. BROWN, JR 2,573,538

HEAT EXCHANGER CONDUIT HAVING INTERNAL. FINS Filed April 10, 1947 2 SHEETS-SHEET 2 A 7* 7+ ee 44 F ,r ,y 54/y 32} FIG. 5

INVENTOR. JOH N W. BROWN JR.

ATTORNEYS.

Patented Oct. 30, 1951 HEAT EXCHANGER ooNnUrr HAVING INTERNAL FINS John W. Brown, Jr., Lakewood, Ohio, assignor to Brown Fintube Company, Elyria, Ohio, at corporation of Ohio Application April 10, 1947, Serial No. 740,598

3 Claims.

This invention relates to heat exchange conduits or tubes adapted to be used with commodities, such as gases, that have low coeificients of heat transfer. More particularly it relates to heat exchange conduits that are provided with internal fins to give them extended internal surface area and which are subject to greater pressures on their exterior than on the inside of the exchanger wall.

My copending application executed of even date herewith, Serial No. 740,597 filed April 10, 1947, which has been abandoned, and assigned to my present assignee, illustrates a type of boiler construction that preferably embodies a heat exchange conduit of the type contemplated by the present invention. In such a boiler, a plurality of heat exchange conduits pass through a body of water that is heated by transfer of heat to it from hot gases on the inside of the conduits. To insure a high rate of heat transfer, the interior of each conduit is provided with a plurality of fins by which the heat from the commodity is transferred to the side walls and from the side walls to the water. If steam is generated in the boiler, the pressure exerted by the steam is ordinarily much greater than the pressure of the commodity within the heat exchange conduit, thus resulting in the application of forces on the exterior walls that may crush them inwardly. Although the example of a conduit used in a boiler has been employed herein to illustrate the invention, it will be understood that the present invention is susceptible of a variety of other uses in which a heat exchange conduit that is resistant to external forces is required.

It is a general object of the present invention to provide a heat exchange conduit with a high rate of heat exchange efliciency and that is strongly reinforced against compressive forces applied at the exterior of the walls. Another object of the invention is to provide a heat exchange conduit with an improved form of heat exchange fin construction on the interior thereof and in efficient heat transfer relation with the side walls. Still another object of the invention is to provide such a fin construction that of itself possesses great compressive strength to support the side walls against high external loads. A still further object of the invention is to provide a heat exchange conduit in which the fins may be bonded to one or more of the walls before the walls are assembled to provide a closed unit. Still an additional object of the invention is to provide a heat exchangeconduit that may be manufactured rapidly and economically.

Further objects and advantages of the invention will become apparent from the following description of a preferred form thereof, reference being made to the accompanying drawings. The essential characteristics of the invention are summarized in the claims.

Referring to the drawings: Figure 1 illustrates a heat exchange conduit embodying the present invention mounted as a vertical fire tube in a boiler; Figure 2 is a perspective of a preferred form of heat exchange conduit with the internal fins in place; Figure 3 is an enlarged section through the conduit of Figure 2 as indicated by the lines 3-3 thereon, showing a modified form of fin construction; Figure 4 is a section similar to Figure 3 but showing a further modified form of fin construction and also a modified form of end wall construction; Figure 5 is a section similar to Figure 4 showing a heat exchange conduit with internal and external heat exchange fin members; and Figure 6 is a further modified form of heat exchanger shown in section similar to the section of Figure 4.

To provide efficient heat interchange for gases or similar commodities having low coefficients of heat transfer, it is necessary to have large extended surfaces for contact with the gases within the conduit. It is also desirable to provide such a construction that the paths for the flow of heat in the extended surface elements are as short as possible. For economy of contruction, as well as efficiency in heat transfer, it is desirable that the walls of the conduit be as thin as possible consistent with the forces which they are required to withstand. I have found that heat exchange conduits of rectangular cross section with longitudinally extending internal fins are eflicient from a heat exchange standpoint in-that they can be constructed with fins of ample surface area to give the required heat exchange capacity; by the use of rectangular sections, the paths for the flow of heat within the fins themselves may be kept at a minimum, while at the same time the-fins can be distributed substantially uniformly throughout the entire interior of the conduits, and so-called shortcircuiting" of any substantial portion of the fluid flowing within the conduit can be eliminated.

The use of rectangular sections, however, presents problems in the construction of conduits that are adapted to withstand external pressures. According to the present invention, the internal fins, which provide the extended heat exchange surface, are utilized to reinforce the conduits against external forces. The internal fins serve the dual purpose of acting as heat transfer surfaces as well as mechanical reinforcements, and thus I am able to provide at reasonable cost conduits which are highly efficient from a heat transfer standpoint and which can be made of relatively light gauge materials and yet have strength to withstand substantial external pressures.

A preferred form of the present invention comprises a closed conduit of generally rectangular cross section formed by placing the outer side edges of two similar pan members in contact with each other and welding them together. Fins are welded or otherwise bonded to the conduit walls to transfer heat efficiently to them from the commodity flowing therethrough. The precise form of the fins may vary in accordance with the following description and as illustrated in the drawings. If desired, heat transfer members may be placed on the exterior of the conduit to perform a heat transfer function on'the outside similar to that which the fins perform on the inside.

The internal fins are not only characterized by a highly efiicient rate of heat transfer to the side walls but by great strength in compression to reinforce the conduit and prevent its being. crushed when high pressures are present on the exterior and low pressures on the interior. To permit ready assembly of the complete conduit, the present invention provides for securing all the fin elements to their supporting conduit walls prior to the assembly of the walls and then final- 1y welding or other wise bonding the walls together to provide the completed conduit.

Referring now to the drawings and particularly to Figure 1, there is illustrated a fire tube boiler that in general is similar to the construction described and claimed in my copending application referred to above. In this figure, the boiler is illustrated as a circular steel container l mounted above a fire box |2. This boiler comprises a circular side wall l3, end walls l4 and I5 and an inner wall l6. Water is admitted to the boiler at I! and removed either as hot water or as steam at l8.

Passing vertically through the boiler and secured in the ends l4 and I5 by welds 20 and 2| are steel heat exchange conduits 25. These conduits act as fire tubes to receive hot gases from the fire box at end 27 and allow them to pass upwardly and out at 28. During the course of their travel, the hot gases give up their heat through the walls of the conduits 25 to heat the water in the boiler Ill. As the water becomes heated, and particularly if large amounts of steam are generated, pressure on the outside of the conduits will greatly exceed that on the inside and will tend to crush the walls thereof inwardly and collapse them.

The inside of each conduit 25 is strongly reinforced against any crushing forces by fins that also act to improve the rate of heat transfer between the commodity on the inside and the commodity on the outside of the conduit. These fins may take several forms, but in general are characterized by great strength in compression and a high heat transfer efliciency.

A preferred form of heat exchange conduit is illustrated in Figure 2. In that figure, the steel walls of the conduit are shown to comprise a of shallow open-ended pans 30 and 32, each provided with end walls or flanges 33 and 34 that terminate in lips or flanges 35 and 36 parallel to the pan bottoms. As hereafter described, the

pans are welded or otherwise bonded together at the contacting faces of the flanges 35 and 36. This construction forms a metal conduit of 'generally rectangular cross section with pair of opposed side walls 40 and 4| formed by the fiat bottoms of the pans 30 and 32 and end walls 43 and 44 formed by the joined upstanding portions 33 and 34 of the pans 30 and 32. In the embodiment of the invention shown in Figure 1, the conduit of Figure 2 extends vertically through the boiler l0, and the exterior walls of the conduit are, as stated above, secured by welds at 20 and 2| to the ends of the boiler.

The commodity, flue gas, that enters the conduit at 21 (Figure l) is a material with a relatively low coefficient of heat transfer and generally travels through at a low pressure. To transfer the heat in this commodity to the commodity surrounding the exterior surface of the conduit and to reinforce the conduit in compression, an improved form of internal fin construction is provided.

One form of finned construction is shown in Figure 2 and is made up of a series of relatively stifi steel channel members each with an outstanding fin portion 50 comprising one or more relatively stifl fins 5| formed integral with a base portion 52. The base portions are welded to the side walls 40 and 4| by a series of resistance welds 54 which maybe made with a conventional seam welder embodying roller electrodes; one electrode bearing against the exterior of a side wall 40 or 4|, and the complementary electrode riding inside of the channel against the base portion 52. The electrodes are urged together in a well-known manner, and sufiicient current is passed from one to the other to make the welds. It will be seen in Figure 2 that alternate channels of a series are welded to the side wall 40 while the intermediate channels are welded to the side wall 4|. By this construction, heat in substantially equal amounts is transferred to each of the side walls to achieve a uniform heat transfer over the exterior surface of the heat exchange conduit. The outer edges of the fin portions 5|, remote from their base 52, are not secured to the side walls adjacent which they terminate but merely abut them to take a, compression load applied to the exterior of the unit.

From the description thus far it will be seen that all of the channels carried by the side wall 40 and all of those'carried by the side wall 4| may be properly located by suitable jigs and welded in place before the pans 30 and 32 are secured together. After the channels have been welded in place on their respective side walls the pans 30 and 32 are assembled as shown in Figure 2 and welded together at their flanges 35 and 36.

The compressive strength of the completed assembly is attained by the presence of the stiff metal fin portions 5| that are secured to one side wall and at their free edges are positioned with relation to the other side wall to engage it and prevent the walls from being forced together under compressive loading. The end walls indicated at 33 and 34 are thick in proportion to their width and also are slightly convex outwardly to form a modified arch and insure the requisite compressive strength required for the uses contemplated.

A modified form of construction in which the walls 43 and 44 are interconnected and further braced to improve their strength in compression is illustrated in Figure 3. In this construction a flat steel plate 60 extends across the conduit 25 parallel to the side walls 40 and 4| and preferably is welded in place between the flanges 35 and 36 of the pans. While it is preferred to weld plate Bil in place it-may be secured in position in any desired manner, as by a force fit.- This construction reinforces the intermediate side walls 33 and 34 and prevents their being crushed inwardly under external pressures.

The plate 68 divide the construction of Figure 3 into two conduits that are used in parallel together to transmit fluid from one end to the other from a common inlet. No advantage is gained under these conditions if heat exchange fins are secured to the plate 80 and consequently the fins B3 are welded only to the side walls 40 and 4|. The fins are channel shaped and generally conform to the construction shown in Figure 2 except that their sides 64 are somewhat shorter than the corresponding parts 5| of that figure. This is because they need only to span the space between the plate 60 and one of the side walls 40 or 4 I. In this way compressive reinforcement from the side wall 40 to side wall 4| is obtained by transmitting compressive stresses from the side wall 40 through its associated fins 53 to the plate 80 and then through the fins on the opposite side of that plate to the side wall 4|. This construction reinforces the end walls 43 and 44 because the fins also stiffen the plate 60 to prevent it from being flexed if excessive compressive loads are applied to the end walls. Thus a structure is provided in which the end walls and side walls reinforce each other against compressive loads.

The base portions 65 of the fins 63 are welded to their respective side walls 40 or 4| in the same manner as described in connection with the fins illustrated in Figure 2. This welding operation is performed before the complete conduit is assembled after which the two pans 30 and 32 with the fins in place are assembled as shown in Figure 3 with the plate 60 between them. The pans and the plate are then securely welded together in the region of the flanges 35 and 38.

The construction described above in connection with Figures 2 and 3 in which the pans are joined together by welds at the flanges 35 and 36 is best used where the thickness of the material from which the pans are made permits the flanges to be formed easily and resistance welded together. If the thickness of the material from which the pans are made is relatively thicker this form of end wall construction is best replaced by that shown in Figure 4. In this latter construction the somewhat thicker pans are brought together with their edges in abutment and then are welded as indicated at 61. This same form of construction is illustrated in the modifications of Figures 5 and 6 but it will be apparent that it may also be used in the constructions in Figures 2 and 3 if desired. On the other hand the construction shown in Figure 2 employing flanges 35 and 36 may, if desired, be substituted for the weld at 61 in those constructions illustrated in Figures 4, 5 and 6.

The arrangement of fins illustrated in the construction of Figure 4 is a modification over those previously described in that the outwardly extending plate-like portions of the fins carried by one side wall interfit with the corresponding fins carried by the other side wall. Thus it will be seen that a series of fin ill with outwardly extending portions H and base portions 12 are welded to the pans 30 and 32 respectively in the same manner as previously described in connection with Figure 2. When the fins are positioned for welding however, they are so arranged that, except for the end fins of a group, two extending portions ll of two adjacent flns carried by one plate lie within the channel formed by the portions ll of a fin HI carried by the other plate. This permits the inclusion within the con-- duit of a larger extended heat transfer surface than is attained with the construction shown in Figure 2 and also provides an assembly that is somewhat stronger in compression. In the construction of Figure 4 it will be evident that the fin extensions N do not extend into contact with the opposite side wall but only into contact with the base of the particular fln within which they nest.

In certain instances it is desirable to employ heat transfer fins on the exterior of the conduit as well as on the interior and this form of construction is illustrated in Figure 5. Here again the usual pans 30 and 32 are, in the final assembly, welded together as at 61. Internal fins 88 and external fins 8| are welded through their base-portions 82 and 83 to the respective side walls with electrode rollers as described in connection with Figure 2. Several arrangements of fins are possible and the arrangement of the internal fins may conform to any of the others described above. The result of such a construction is to produce a heat exchange conduit that is in all respects similar on its interior to one of the forms already described and that in addition provides an extended heat exchange surface on the exterior thereof.

A further modified form of conduit embodying the present invention is illustrated in Figure 6. In certain features this construction resembles the construction of Figure 4 except that of two fin portions on a channel shaped fin only one portion of any one fin interengages within the channel of an opposite fin channel member. Thus there are secured to the pans channel members 85 and 86 so positioned that the fin 81 of the member 85 lies within the channel of mem- .ber 86 and in turn the fin 88 of the member 86 ing member but extend from the pan to which they are secured across the conduit space into direct contact with the opposing conduit wall.

Thus in each of the channel members 85 and 86 the interfitting fins as indicated at 81 and 88 are somewhat shorter than the free fins 90 because they only extend from one pan across to contact the base of the opposite channel member and so do not extend to the surface of the opposing side wall.

Various other changes and modifications may be made herein without departing from the spirit and scope of my invention. It is therefore to be understood that my patent is not limited to the preferred forms of the invention described herein, or in any other manner than by the scope of the appended claims.

I claim:

1. A heat exchange conduit comprising a hollow structure with a pair of opposed side walls, said opposed side walls each having a plurality of channel shaped fins having base portions welded thereto and fin portions extending toward the opposite side wall, and a plate interposed between the fins carried by one side wall and those carried by the other side wall and engaged by the fin portions of both sets of fins to reinforce the conduit against external pressure.

2. A heat exchange conduit, comprising two relatively shallow pans with short end walls, weld joining the end walls of one pan to those of the other to provide an elongated closed structure of generally rectangular cross section with the bottoms of the pans forming one pair of opposed walls and the joined walls of the pans forming another pair of opposed walls, a plurality of channel shaped heat exchanger fins, each with a base portion and a pair of fin portions, certain of said fins being secured to the bottom of one pan, certain other of said fins being secured to the bottom of the other pan,

' said fin portions extending from their respective bases approximately half way toward the opposite pan bottom, and a plate interposed between the fins carried by one pan bottom and those carried by the other pan bottom.

3. A heat exchange conduit comprising two relatively shallow pans with short end walls, welds joining the end walls of one pan to those of the other to provide an elongated closed structure of generally rectangular cross section with the bottoms of the pans forming one pair of opposed walls and the joined walls of the pans forming another pair of opposed, walls, a plurality of channel shaped heat exchanger fins, each with a base. portion and a pair of fin portions, certain 8 01 said fins being secured to the bottom of one pan, certain other of said fins being secured to the bottom of the other pan, said fin portions extending from their respective bases approximately half way toward the opposite pan bottom, and a plate interposed between the fins carried by one pan bottom and those carried by the other pan bottom, said plate being secured to the said walls formed by the pan end walls adjacent the welds joining said walls.

JOHN W. BROWN, JR.

REFERENCES CITED The following references are of record in the file of this patent: Y

UNITED STATES PATENTS Number Name Date 1,313,730 Pease Aug. 19, 1919 1,775,819 Fischer et a1 Sept. 16, 1930 1,845,073 Bennett Feb. 16, 1932 2,088,391 Steinberg et a1 Jul 27, 1937 2,151,540 Varga Mar. 21, 1939 2,172,667 Nelson Sept. 12, 1939 FOREIGN PATENTS Number Country I Date 265,845 Great Britain Feb. 17, 1927 535,056 Great Britain Mar. 27. 1941 

